We present a systematic theoretical investigation on the overall ground state and excited-state isomerization reaction mechanism of ortho-green fluorescent protein chromophore (o-HBDI) using the density functional theory and the multireference methods. The calculated results and subsequent analysis suggest the possible isomerization mechanism for o-HBDI. By comparison with experimental observation and detailed analysis, it is concluded that as initiated by the excited-state intramolecular proton transfer reaction, the conical intersection between the ground state and the excited state along the C4-C5 single-bond rotational coordinate is responsible for the rapid deactivation of o-HBDI.

The Na-23 quadrupolar coupling constant of the Na+ ion in aqueous solution has been predicted using molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics methods for the calculation of electric field gradients. The developed computational approach is generally expected to provide reliable estimates of the quadrupolar coupling constants of monoatomic species in condensed phases, and we show here that intermolecular polarization and non-electrostatic interactions are of crucial importance as they result in a 100% increased quadrupolar coupling constant of the ion as compared to a simpler pure electrostatic picture. These findings question the reliability of the commonly applied classical Sternheimer approximation for the calculations of the electric field gradient. As it can be expected from symmetry considerations, the quadrupolar coupling constants of the 5- and 6-coordinated Na+ ions in solution are found to differ significantly.

We present periodic ab initio calculations for ferroelectric NaNO2. The spontaneous polarisation (P-s) has been calculated with three different models based on: (i) point charges; (ii) a multipolar expansion of the charge ;distribution; and (iii) the Berry phase approach. Both the Hartree-Fock and LDA Hamiltonians were employed. Within the Hartree-Fock scheme, at the optimised geometry, we obtain P-s values of 20.3, 13.0 and 16.4 muC cm(-2) with the three models, compared to the experimental value of similar to11.9 muC m(-2). The Berry-phase approach at the Hartree-Fock level gives a value very close to experiment ( namely 12 muC cm(-2)) when the experimental structure is used. At the optimised LDA structure, the LDA P-s values are 16.8, 10.0 and 16.9 muC cm(-2) with models (i)-(iii). The optimised lattice parameters at the Hartree-Fock level are slightly shorter (between 0 and 4%) than those determined experimentally from X-ray-diffraction, while the lattice parameters of the LDA-optimised structure are up to 10% smaller than the experiment. The calculated lattice energies are 679 and 964 kJ mol(-1) at the HF and LDA levels, compared with 729 kJ mol(-1) from the experiment. Charge densities, Mulliken charges and dipole moments are discussed. Finally, we have studied the mechanism for the phase transformation in-between the ferroelectric and paraelectric crystal structures; a rotation of the NO2 group around the c-axis gives the lowest energy barrier.

The solvation shell structure and dynamics of a single Cu2+ ion in a periodic box with 32 water molecules under ambient conditions has been investigated using Car-Parrinello molecular dynamics simulations in a time-window of 18 ps. Five-fold coordination with four equidistant equatorial water molecules at 2.00 angstrom and one axial water molecule at 2.45 angstrom from the Cu2+ ion is found. A hole without water molecules is found on the opposite side of the axial water. The ion-water bonding character for the equatorial water molecules is different from that of the axial water molecules, as shown by a localized orbital analysis of the electronic structure. Moreover, the calculated OD stretching vibrational band for the equatorial water molecules lies ca. 175 cm(-1) below the axial-water band, in good agreement with experimental data. The equatorial-water band lies below, and the axial-water band above, the pure liquid D2O band, also in agreement with experimental data.

We report on the encapsulation of the antibiotic clofazimine (CLZ) within the pores of mesoporous silica particles having hydrophilic (CBET value of 137) and more hydrophobic (CBET value of 94 after calcination at 600 °C) surfaces. We studied the effect of pH on the released amount of CLZ in aqueous solutions and observed a maximum at pH 4.1 in correlation with the solubility of the drug. Less release of the drug was observed from the more hydrophobic particles which was attributed to a difference in the affinity of the drug to the carrier particles. Fluorescence lifetime imaging microscopy, emission spectra, and fluorescence lifetimes of single drug loaded particles provided detailed understanding and new knowledge of the physical form of the encapsulated drug and the distribution within the particles. The distribution of CLZ within the particles was independent of the surface chemistry of the particles. The confirmation of CLZ molecules as monomers or aggregates was revealed by controlled removal of the drug with solvent. Additionally, the observed optical "halo effect" in the fluorescent images was interpreted in terms of specific quenching of high concentration of molecules. The emission lifetime experiments suggest stronger interaction of CLZ with the more hydrophobic particles, which is relevant to its release. The results reported in this work demonstrate that tuning the hydrophilicity/hydrophobicity of mesoporous silica particles can be used as a tool to control the release without impacting their loading ability.

This investigation has the primary objective of elucidating the lithium intercalation process in the crystal structure of a new niobium oxyfluoride compound Nb2O2F3. The framework of the density functional theory was applied in a generalized gradient approximation together with the hybrid functional method. It is revealed that lithium atoms intercalate in this material in a maximum concentration of one Li atom per formula unit forming LiNb2O2F3. Moreover, octahedral positions in between the layers of Nb-O-F appear as the Li preferred occupancy resulting in a structural volume expansion of only 5%. Electronic structure evolution with the insertion of lithium displays a transformation from semi-conductor to metal when half of the lithium atoms are added. This transformation occurs due to a symmetry break induced by the transition from the + 8 to + 7 oxidation state of half of the Nb2 dimers. Then, after full lithiation the symmetry is recovered and the material becomes a semiconductor again with a band gap amounting to 1 eV. The evaluated average deintercalation potential reaches 1.29 V vs. Li/Li+ with activation energy for lithium ion migration of 0.79 eV. The computed low potential of the redox reaction Nb-2(8+) to Nb-2(7+) includes niobium oxyfluoride in the map of possible materials for the anode application of Li-ion batteries.

Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, the key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.

Metal-air batteries have become promising candidates for modern energy storage due to their high theoretical energy density in comparison to other storage devices. The lower overpotential of Na compared with Li makes Na-air batteries more efficient in terms of battery lifetime. Additionally, the abundance of Na over Li is another advantage for Na batteries compared to Li batteries. Na2O2 is one of the main products of sodium-air battery reactions. The efficiency of air cells is always related to the charge transport mechanisms in the formed product. To unveil these diffusion mechanisms in one of the main products of the cell reaction Na-O-2 we systematically investigate the mobility of charge carriers as well as the electronic structural properties of sodium peroxide. The framework of the density functional theory based on hybrid functional approach is used to study the mobility of charge carriers and intrinsic defects in Na2O2. Our calculations reveal that the formation of small electron and hole polarons is preferentially occurring over the delocalized state in the crystal structure of Na2O2. The migration of these small polarons displays activation energies of about 0.92 eV and 0.32 eV for the electron and hole polarons respectively, while the analysis of the charged sodium vacancy mobility reveals an activation energy of about 0.5 eV. These results suggest that the charge transport in sodium peroxide would mainly occur through the diffusion of hole polarons.

Sodium-ion-based batteries have evolved as excellent alternatives to their lithium-ion-based counterparts due to the abundance, uniform geographical distribution and low price of Na resources. In the pursuit of sodium chemistry, recently the alluaudite framework Na2M2(SO4)(3) has been unveiled as a high-voltage sodium insertion system. In this context, the framework of density functional theory has been applied to systematically investigate the crystal structure evolution, density of states and charge transfer with sodium ions insertion, and the corresponding average redox potential, for Na2M2(SO4)(3) (M = Fe, Mn, Co and Ni). It is shown that full removal of sodium atoms from the Fe-based device is not a favorable process due to the 8% volume shrinkage. The imaginary frequencies obtained in the phonon dispersion also reflect this instability and the possible phase transition. This high volume change has not been observed in the cases of the Co- and Ni-based compounds. This is because the redox reaction assumes a different mechanism for each of the compounds investigated. For the polyanion with Fe, the removal of sodium ions induces a charge reorganization at the Fe centers. For the Mn case, the redox process induces a charge reorganization of the Mn centers with a small participation of the oxygen atoms. The Co and Ni compounds present a distinct trend with the redox reaction occurring with a strong participation of the oxygen sublattice, resulting in a very small volume change upon desodiation. Moreover, the average deintercalation potential for each of the compounds has been computed. The implications of our findings have been discussed both from the scientific perspective and in terms of technological aspects.

The electronic structure, absorption and emission spectra, aromaticity and photophysical behavior of the recently synthesized tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene compounds have been studied computationally. Both compounds demonstrate a specific bifacial aromaticity, which is unusual for hetero[8]circulenes; the inner eight-membered core sustains an expected strong paratropic magnetically-induced ring current, while the outer perimeter contains saturated Si(Et)(2) and Ge(Et)(2) moieties which break the conjugation between the thiophene rings. The overall magnetically-induced ring current for both studied circulenes is close to zero because of the strong local diatropic currents in each thiophene ring that compensate the paratropic counterpart. The electronic absorption and emission spectra of tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene demonstrate a clear visible vibronic progression. The 0-0 band is the most active one in the absorption spectra, while in the fluorescence spectra the 0-1 band composed of several normal vibrations is more intense compared with the 0-0 band in excellent agreement with experiment. Accounting for spin-orbit coupling effects, an analysis of the photophysical constants for the two compounds demonstrates: (1) a clear manifestation of the internal heavy atom effect on the inter-system crossing efficiency; (2) one to two order domination of non-radiative rates over the fluorescence rate; and (3) that the S-1-S-0 internal conversion is extremely slow and can not compete with the fluorescence, while the S-1-T-n inter-system crossing is a main deactivation channel of the S-1 excited state. These results provide new insight into the electronic structure and photophysics of tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene as novel standalone representatives of hetero[8]circulenes - tetraannelated derivatives of tetrathienylene.

In the present work, we studied the synergetic effect of benzoannelation and NH/O-substitution for enhancing the absorption intensity in a series of novel designed benzoannelated aza- and oxa[8]circulenes. Semi-empirical estimations of the fluorescence rate constants allowed us to determine the most promising fluorophores among all the possible benzoannelated aza-, oxa- and mixed azaoza[8]circulenes. Among them, para-dibenzoannelated [8]circulenes demonstrated the most intense light absorption and emission due to the prevailing role of the linear acene chromophore. Calculated phi(fl) values are in complete agreement with experimental data for a number of already synthesized circulenes. Thus, we believe that the most promising circulenes designed in this study can demonstrate an intensive fluorescence in the case of their successful synthesis, which in turn could be extremely useful for the fabrication of future blue OLEDs. Special attention is devoted to the aromaticity features and peculiarities of the absorption spectra for the two highly-symmetrical (D-4h ground state symmetry) pi-isoelectronic species as well as the so-called tetrabenzotetraaza[8]circulene and tetrabenzotetraoxa[8]circulene molecules. Both of them are characterized by rich electronic spectra, which can be assigned only by taking into account the vibronic coarse structure of the first electronic absorption band; the 0-1 and 0-2 transitions were found to be active in the absorption spectrum in complete agreement with experimental data obtained for both energy and intensity. The corresponding promotive vibrational modes have been determined and their vibronic activity estimated using the Franck-Condon approximation.

Magnetically induced current densities and current pathways have been calculated for a series of fully annelated dicationic and dianionic tetraphenylenes, which are also named [8]circulenes. The gauge including magnetically induced current (GIMIC) method has been employed for calculating the current density susceptibilities. The aromatic character and current pathways are deduced from the calculated current density susceptibilities showing that the neutral [8]circulenes have two concentric pathways with aromatic and antiaromatic character, respectively. The inner octatetraene core (the hub) is found to sustain a paratropic (antiaromatic) ring current, whereas the ring current along the outer part of the macrocycle (the rim) is diatropic (aromatic). The neutral [8]circulenes can be considered nonaromatic, because the sum of the ring-current strengths of the hub and the rim almost vanishes. The aromatic character of the doubly charged [8]circulenes is completely different: the dianionic [8]circulenes and the OC-, CH-, CH2-, SiH-, GeH-, SiH2-, and GeH2-containing dicationic species sustain net diatropic ring currents i.e., they are aromatic, whereas the O-, S-, Se-, NH-, PH- and AsH-containing dicationic [8]circulenes are strongly antiaromatic. The present study also shows that GIMIC calculations on the [8]circulenes provide more accurate information about the aromatic character than that obtained using local indices such as nuclear-independent chemical shifts (NICSs) and H-1 NMR chemical shifts.

This communication presents a structure-property study of a few novel pyridine-based difluoroborate compounds with a N-BF2-O core, which exhibit outstanding fluorescence properties. To exploit their potential for two-photon bioimaging, relationships between the two-photon action cross section and systematic structural modifications have been investigated and unravelled.

Recently, cobalt redox electrolyte mediators have emerged as a promising alternative to the commonly used iodide/triiodide redox shuttle in dye-sensitized solar cells (DSCs). Here, we report the successful use of a new quasi-liquid, polymer-based electrolyte containing the Co3+/Co2+ redox mediator in 3-methoxy propionitrile solvent in order to overcome the limitations of high cell resistance, low diffusion coefficient and rapid recombination losses. The performance of the solar cells containing the polymer based electrolytes increased by a factor of 1.2 with respect to an analogous electrolyte without the polymer. The performances of the fabricated DSCs have been investigated in detail by photovoltaic, transient electron measurements, EIS, Raman and UV-vis spectroscopy. This approach offers an effective way to make high-performance and long-lasting DSCs.

This study is focused on eight structurally analogous natural flavonoids that exhibit a wide range of biological activities, which are of interest in pharmacy, cosmetics and the food industry. Using both experimental and theoretical approaches, we relate their fundamental physico-chemical properties to the structural motifs, with particular focus on UV/Vis absorption properties and pH dependence. We highlight the role of the C2-C3 double bond, whose presence or absence is responsible for the switch between absorption bands in the UVB and UVA regions, which is rationalized by strong modification of the involved molecular orbitals. After deprotonation in an alkaline environment, a typical switch in intensity at the maximum absorption wavelength (lambda(max)) is observed enabling the calculation of pK(a) values for compounds with a C2-C3 single bond, whereas a bathochromic shift of lambda(max) vs. pH is observed for the C2-C3 double bond containing compounds. These behaviors are also rationalized and understood by MO analysis. Interestingly, high pH (above 11 for ampelopsin and above 9 for myricetin) induces the formation of a long-wavelength peak arising from double and/or triple deprotonation. Substitution at position C3 by the OH group has almost no effect on lambda(max) for taxifolin and eriodictyol, whereas the effect is larger for quercetin and luteolin. An additional sugar moiety at C3 has a stabilizing effect and induces only minor changes in spectral behavior.

The temperature-dependent properties of pre-adsorbed layers of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) were investigated on silica and hydrophobized silica surfaces. Three different techniques, quartz crystal microbalance with dissipation monitoring, ellipsometry, and atomic force microscopy imaging, were used, providing complementary and concise information on the structure, mass and viscoelastic properties of the polymer layer. Adsorption was conducted at 25 degrees C, followed by a rinsing step. The properties of such pre-adsorbed layers were determined as a function of temperature in the range 25 degrees C to 50 degrees C. It was found that the layers became more compact with increasing temperature and that this effect was reversible, when decreasing the temperature. The compaction was more prominent for MC, as shown in the AFM images and in the thickness data derived from the QCM analysis. This is consistent with the fact that the phase transition temperature is lower, in the vicinity of 50 degrees C, for MC than for HPMC. The water content of the adsorbed layers was found to be high, even at the highest temperature, 50 degrees C, explored in this investigation.

A new ambient- pressure metastable single- bonded 3D nitrogen allotrope (TrigN) of trigonal symmetry (space group R(-)3) was calculated using density functional theory (DFT). A comprehensive characterization of this material, comprising thermodynamic, elastic, and spectral (vibrational, UV-vis absorption, and nuclear magnetic resonance) properties, was performed. Using high-throughput band structure calculation, the TrigN phase was characterized as an insulator with an indirect band gap of 2.977 eV. Phonon dispersion calculations justified that this structure is vibrationally stable at ambient pressure. The calculated Raman activities at the Gamma-point demonstrated a rich pattern, whereas no relatively intense transitions were observed in its IR absorption spectrum. The TrigN material is almost transparent to visible light as well as to ultraviolet A and B. The main absorption peaks appeared within the range of 50-200 nm. The electron arrangement of the nitrogen nuclei in the studied nitrogen allotrope is much denser compared to that of the molecular nitrogen, which is in agreement with the calculated magnetic shielding tensor values. Robust mechanical stability is revealed from the elastic constants calculation. Due to strong anisotropy, the values of the Young's moduli vary from 281 to 786 GPa. A huge amount of internal energy is enclosed in the TrigN material. Upon decomposition to molecular nitrogen, the energy release is expected to be 11.01 kJ g(-1) compared to the value of 10.22 kJ g(-1) for the cubic gauche form of nitrogen. The TrigN allotrope possesses unique detonation characteristics with a detonation pressure of 146.06 GPa and velocity of 15.86 km s(-1).

The binding of zinc (Zn) ions to proteins is important for many cellular events. The theoretical and computational description of this binding (as well as that of other transition metals) is a challenging task. In this paper the binding of the Zn ion to four cysteine residues in the structural site of horse liver alcohol dehydrogenase (HLADH) is studied using a synthetic peptide mimic of this site. The study includes experimental measurements of binding constants, classical free energy calculations from molecular dynamics (MD) simulations and quantum mechanical (QM) electron structure calculations. The classical MD results account for interactions at the molecular level and reproduce the absolute binding energy and the hydration free energy of the Zn ion with an accuracy of about 10%. This is insufficient to obtain correct free energy differences. QM correction terms were calculated from density functional theory (DFT) on small clusters of atoms to include electronic polarisation of the closest waters and covalent contributions to the Zn-S coordination bond. This results in reasonably good agreement with the experimentally measured binding constants and Zn ion hydration free energies in agreement with published experimental values. The study also includes the replacement of one cysteine residue to an alanine. Simulations as well as experiments showed only a small effect of this upon the binding free energy. A detailed analysis indicate that the sulfur is replaced by three water molecules, thereby changing the coordination number of Zn from four (as in the original peptide) to six (as in water).

The single atom alloy of extended surfaces is known to provide remarkably enhanced catalytic performance toward heterogeneous hydrogenation. Here we demonstrate from first principles calculations that this approach can be extended to nanostructures, such as bimetallic nanoparticles. The catalytic properties of the single-Pd-doped Cu-55 nanoparticles have been systemically examined for H-2 dissociation as well as H atom adsorption and diffusion, following the concept of single atom alloy. It is found that doping a single Pd atom at the edge site of the Cu-55 shell can considerably reduce the activation energy of H-2 dissociation, while the single Pd atom doped at the top site or in the inner layers is much less effective. The H atom adsorption on Cu-55 is slightly stronger than that on the Cu(111) surface; however, a larger nanoparticle that contains 147 atoms could effectively recover the weak binding of the H atoms. We have also investigated the H atom diffusion on the 55-atom nanoparticle and found that spillover of the produced H atoms could be a feasible process due to the low diffusion barriers. Our results have demonstrated that facile H-2 dissociation and weak H atom adsorption could be combined at the nanoscale. Moreover, the effects of doping one more Pd atom on the H-2 dissociation and H atom adsorption have also been investigated. We have found that both the doping Pd atoms in the most stable configuration could independently exhibit their catalytic activity, behaving as two single-atom-alloy catalysts.

The energy loss in dye-sensitized solar cells calculated from the energy difference between the lowest electronic transition of the dye and the obtained open-circuit voltage is often 1 eV or even more. To minimize this loss, it is important to accurately determine the energy alignment at the TiO(2)/dye/redox-mediator interface. In this study, we compared the results from electrochemistry and photoelectron spectroscopy for determining the energy alignment of three rylene dyes, two of which absorb relatively far in the red. The trends observed with the methods were different, as in the former, the energy alignment is measured relative to an external reference and includes contributions from solvent reorganization energies, while in the latter, it is measured relative to the energetics of the TiO(2) and is lacking such contributions. The influence of the dyes' dipole moments on the energetics of the TiO(2) was also measured and explained some of the differences in trends. Finally, we compared the injection efficiencies of the two red-absorbing dyes and found that the differences in injection efficiencies can be better explained using the energy alignment determined from photoelectron spectroscopy. This shows that the method for measuring the energetics of a DSC should be chosen according to what process one intends to study.

Means to measure the temporal evolution following a photo-excitation in conjugated polymers are a key for the understanding and optimization of their function in applications such as organic solar cells. In this paper we study the electronic structure dynamics by direct pump-probe measurements of the excited electrons in such materials. Specifically, we carried out a time-resolved photoelectron spectroscopy (TRPES) study of the polymer PCPDTBT by combining an extreme ultraviolet (XUV) high harmonic generation source with a time-of-flight spectrometer. After excitation to either the 1st excited state or to a higher excited state, we follow how the electronic structure develops and relaxes on the electron binding energy scale. Specifically, we follow a less than 50 fs relaxation of the higher exited state and a 10 times slower relaxation of the 1st excited state. We corroborate the results using DFT calculations. Our study demonstrates the power of TRPES for studying photo-excited electron energetics and dynamics of solar cell materials.

The present work addresses isotropic hyperfine coupling constants in polyatomic systems with a particular emphasis on a largely neglected, but a posteriori significant, effect, namely zero-point vibrational corrections. Using the density functional restricted-unrestricted approach, the zero-point vibrational corrections are evaluated for the allyl radical and four of its derivatives. In addition for establishing the numerical size of the zero-point vibrational corrections to the isotropic hyperfine coupling constants, we present simple guidelines useful for identifying hydrogens for which such corrections are significant. Based on our findings, we critically re-examine the computational procedures used for the determination of hyperfine coupling constants in general as well as the practice of using experimental hyperfine coupling constants as reference data when benchmarking and optimizing exchange-correlation functionals and basis sets for such calculations.

Three new phenothiazine dyes were designed and synthesized, utilizing different acceptor groups. Upon application to TiO2-based solar cells, the effects of different acceptors on the photophysical and electrochemical properties of the dyes and the solar cell performance are detailed. The introduction of a pyridinium unit or 5-carboxy-1-hexyl-2,3,3-trimethyl-indolium unit into the molecular frame as the acceptor instead of cyano acrylic acid can effectively cause a red shift in the absorption spectra. Applied to DSSCs, the devices sensitized by CM502 with the pyridinium unit as the acceptor show the highest efficiency of 7.3%. The devices fabricated with dye CM501 with cyano acrylic acid as the acceptor exhibited the highest V-oc while for the devices sensitized by the dye CM503 with 5-carboxy-1-hexyl2,3,3- trimethyl-3H-indolium unit as the acceptor, the Voc value was the lowest, at 494 mV. The addition of TBP in the electrolyte can improve the performance of DSSCs fabricated using CM501 and CM502, with the Voc value greatly improved but the J(sc) value slightly decreased. However, with the addition of TBP in the electrolyte, the efficiency of the cells sensitized by CM503 dropped significantly (from 4.9% to 1.0% when 0.1 M TBP was added).

In the present study, tetramethylammonium hydroquinone (HQ)/benzoquinone (BQ) were developed for use as a redox couple, with poly(3,4-ethylenedioxythiophene) (PEDOT) and multiwalled carbon nanotubes (MWNT) being proposed for use as counter electrode (CE) catalysts in dye-sensitized solar cells (DSSCs). Both metal-complex N719 and metal-free organic dye CM309 were employed to fabricate devices. For the devices sensitized by N719, when using PEDOT and MWNT CEs, power conversion efficiencies (PCE) of 5.2 and 4.9% were obtained, respectively, which were much higher than that of the device using the traditional Pt CE (4.7%) when HQ/BQ electrolyte was employed. However, with the HQ/BQ redox shuttle, the efficiency of the devices sensitized by N719 is much lower than that of the devices when the traditional I-/I-3(-) based electrolyte and Pt CE were employed (7.9%). While for the CM309 sensitized solar cells, when the HQ/BQ redox shuttle was employed, PEDOT and MWNT performed much better than Pt, the DSSC using the PEDOT CE showed an efficiency of 6.2%, which was close to that of the DSSC using the traditional I-/I-3(-) electrolyte and Pt CE (6.3%).

Surface science, which spans the fields of chemistry, physics, biology and materials science, requires information to be obtained on the local properties and property variations across a surface. This has resulted in the development of different scanning probe methods that allow the measurement of local chemical composition and local electrical and mechanical properties. These techniques have led to rapid advancement in fundamental science with applications in areas such as composite materials, corrosion protection and wear resistance. In this perspective article, we focussed on the branch of scanning probe methods that allows the determination of surface nanomechanical properties. We discussed some different AFM-based modes that were used for these measurements and provided illustrative examples of the type of information that could be obtained. We also discussed some of the difficulties encountered during such studies.

Short-range interactions between surfactant and lipid layers are of great importance in technical applications in complex fluids such as foams, dispersions and emulsions, as well as in the formulation and performance of dispersants, detergents and flocculants. It is also of utmost importance in biological systems where interactions between biomembranes influence a range of processes. The field of short-range interactions has been thoroughly investigated during the past 30 years, following the emergence of a number of techniques to measure interaction forces, Thus, our understanding has increased considerably and it is timely to summarize relevant knowledge accumulated in this area. In this review we focus on the nature of short-range interactions between non-ionic and zwitterionic surfactant and lipid layers exposing their polar groups to the surrounding medium. We discuss the complex interplay of short-range (van der Waals, hydration, steric and other) forces based on recent theoretical and experimental results.

Atomic force microscopy (AFM) reveals that tribotronic control of friction using an external potential applied to a gold surface is possible for ionic liquid (IL) concentrations as low as 5 mol% in hexadecane. The IL used is trihexyl(tetradecyl) phosphonium bis(2,4,4-trimethylpentyl)phosphinate, in which both the cation and anion have surfactant-like structures, and is miscible with hexadecane in all proportions. For IL concentrations less than 5 mol% friction does not vary with applied potential, but for 5 mol% and above changing the potential changes the composition of the IL boundary layer from cation-enriched (negative potentials) to anion-enriched (positive potentials). As the lubricities of the cation-rich and anion-rich boundary layers differ, this enables active control of friction in oil-based lubricants.

Ferroelectrics find broad applications, e.g. in non-volatile memories, but the switching kinetics in real, disordered, materials is still incompletely understood. Here, we develop an electrostatic model to study ferroelectric switching using 3D Monte Carlo simulations. We apply this model to the prototypical small molecular ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA) and find good agreement between the Monte Carlo simulations, experiments, and molecular dynamics studies. Since the model lacks any explicit steric effects, we conclude that these are of minor importance. While the material is shown to have a frustrated antiferroelectric ground state, it behaves as a normal ferroelectric under practical conditions due to the large energy barrier for switching that prevents the material from reaching its ground state after poling. We find that field-driven polarization reversal and spontaneous depolarization have orders of magnitude different switching kinetics. For the former, which determines the coercive field and is relevant for data writing, nucleation occurs at the electrodes, whereas for the latter, which governs data retention, nucleation occurs at disorder-induced defects. As a result, by reducing the disorder in the system, the polarization retention time can be increased dramatically while the coercive field remains unchanged.

Vertical excitation energies and transition dipole moments between excited electronic states have been calculated for the trans-polyenes series C4H6-C12H14 in order to study the formation of excited state absorption spectra of these species. Quadratic response theory is applied in conjunction with the self-consistent field method and a hierarchical set of coupled-cluster methods. The convergence of the excited state absorption, with respect to wavefunction and treatment of electron correlation and also the length of the oligomer unit, is studied, revealing a considerable demand on the computational effort in order to predict the excited state spectra with precision. The organization of the excited states is found to change in character along the polyene series. The inflexion point for the vertical excitation energies between the one-photon allowed 1(1)B(u) and the two-photon 2(1)A(g) state is predicted to occur between hexatriene and octatetraene. Good agreement with experiment is obtained for butadiene and hexatriene for which the most accurate calculations have been carried out.

Excitation energies and transition dipole moments between excited electronic states have been calculated using various theoretical methods to investigate the ability to describe excited state absorption. Quadratic response theory is used in combination with self-consistent field, multi-configurational self-consistent field, and coupled-cluster electronic structure methods. The results of these different methods are compared. The set of molecules considered includes lithium hydride, carbon monoxide, formaldehyde, formamide, and sym-tetrazine. For some of the molecules results are also compared with the method of applying linear response theory to an excited state wavefunction separately optimized by means of the multi-configurational self-consistent field method.

Excitation energies and transition dipole moments between excited electronic states have been calculated using various theoretical methods to investigate the ability to describe excited state absorption. Quadratic response theory is used in combination with self-consistent field, multi-configurational self-consistent field, and coupled-cluster electronic structure methods. The results of these different methods are compared. The set of molecules considered includes lithium hydride, carbon monoxide, formaldehyde, formamide, and symtetrazine. For some of the molecules results are also compared with the method of applying linear response theory to an excited state wavefunction separately optimized by means of the multi-configurational self-consistent field method.

Vertical excitation energies and transition dipole moments between excited electronic states have been calculated for the trans-polyenes series C 4H 6-C 12H 14 in order to study the formation of excited state absorption spectra of these species. Quadratic response theory is applied in conjunction with the self-consistent field method and a hierarchical set of coupled-cluster methods. The convergence of the excited state absorption, with respect to wavefunction and treatment of electron correlation and also the length of the oligomer unit, is studied, revealing a considerable demand on the computational effort in order to predict the excited state spectra with precision. The organization of the excited states is found to change in character along the polyene series. The inflexion point for the vertical excitation energies between the one-photon allowed 1 1B u and the two-photon 2 1A g state is predicted to occur between hexatriene and octatetraene. Good agreement with experiment is obtained for butadiene and hexatriene for which the most accurate calculations have been carried out.

It has been long recognized that the surface chemistry of silica, and in particular the type and relative amount of surface bound silanol groups, plays a critical role in many of the properties associated with the material, where a typical example is the discrepant adsorption behavior observed depending on the pretreatment history of the surface. However, in spite of its importance, the direct probing of specific surface silanol groups under water has been hampered by instrumental limitations. Here we make use of vibrational sum frequency spectroscopy (VSFS) to first, identify under water the OH stretch of isolated surface silanols, and second, explore its acid/base behavior and dependence on the surface pretreatment method. The properties of other types of silanol groups (i.e. hydrogen bonded/geminal) are also inferred from the data. The ability to directly probe these functional groups under water represents a crucial step to further improving our understanding of this widely used mineral oxide.

Comprehensive understanding of the charge transport mechanism in the intrinsic structure of an electrode material is essential in accounting for its electrochemical performance. We present here systematic experimental and theoretical investigations of Li+-ion diffusion in a novel layered material, viz. lithium titanium niobate. Lithium titanium niobate (exact composition Li0.55K0.45TiNbO5 center dot 1.06H(2)O) is obtained from sol-gel synthesized potassium titanium niobate (KTiNbO5) by an ion-exchange method. The Li+-ions are inserted and de-inserted preferentially into the galleries between the octahedral layers formed by edge and corner sharing TiO6 and NbO6 octahedral units and the effective chemical diffusion coefficient, is estimated to be 3.8 x 10(-11) cm(2) s(-1) using the galvanostatic intermittent titration technique (GITT). Calculations based on density functional theory (DFT) strongly confirm the anisotropic Li+-ion diffusion in the interlayer galleries and that Li+-ions predominantly diffuse along the crystallographic b-direction. The preferential Li+-ion diffusion along the b-direction is assisted by line-defects, which are observed to be higher in concentration along the b-direction compared to the a-and c-directions, as revealed by high resolution electron microscopy. The Li-Ti niobate can be cycled to low voltages (approximate to 0.2 V) and show stable and satisfactory battery performance over 100 cycles. Due to the possibility of cycling to low voltages, cyclic voltammetry and X-ray photoelectron spectroscopy convincingly reveal the reversibility of Ti3+ <-> Ti2+ along with Ti4+ <-> Ti3+ and Nb5+ <-> Nb4+.

We have performed Car-Parrinello molecular dynamics simulations at ambient conditions for four-, five- and six-coordinated Cu(II) aqua complexes. The molecular geometry has been investigated in terms of Cu-O, Cu-H bond lengths and O-Cu-O bond angles and compared with earlier experimental measurement results and theoretical calculations. We find that the average Cu-O and Cu-H bond lengths increase with increasing coordination number. We have also observed relatively faster structural transition in the case of five- coordinated complex between trigonal bipyramidal and square pyramidal geometry. This result deviates from the findings of the earlier report (A. Pasquarello et al., Science, 2001, 291, 856) on copper( II) in aqueous solution and we attribute these differences to the neglect of solvent environment in our calculations. The averaged absorption spectra for the copper( II) aqua complexes have been computed using spin-restricted density functional linear response formalism taking 100 snap shots from a trajectory of 0.48 ps. We find that the calculated spectra are significantly different, showing clear features that distinguish each coordination model. Comparison with the experimentally reported absorption spectra is made wherever it is possible and the results obtained favor the distorted fivefold-coordination arrangement for the molecular structure of the Cu(II) ion in aqueous solution.

We present a combined investigation by means of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy of condensed multilayers of two polyphenylsiloles, namely hexaphenylsilole (HPS) and tetraphenylsilole (TPS). Both compounds exhibit very similar spectroscopic signatures, whose interpretation is aided by density functional theory (DFT) calculations. High-resolution XPS spectra of the Si 2p and C 1s core levels of these multilayers indicate a positively charged silicon ion flanked by two negatively charged adjacent carbon atoms in the silole core of both molecules. This result is corroborated quantitatively by DFT calculations on isolated HPS (TPS) molecules, which show a natural bond orbital partial charge of + 1.67 e (+1.58 e) on the silicon and -0.34 e (-0.58 e) on the two neighbouring carbon atoms in the silole ring. These charges are conserved in direct contact with a Cu(111) substrate for films of submonolayer coverage, as evidenced by the Si 2p XPS data. The C K-edge NEXAFS spectra of HPS and TPS multilayers exhibit distinct and differing features. Their main characteristics reappear in the simulated spectra and are assigned to the different inequivalent carbon species in the molecule. The angle-dependent measurements hardly reveal any dichroism, i.e., the molecular p-systems are not uniformly oriented parallel or perpendicular with respect to the surface. Changes in the growth conditions of TPS, i.e., a reduction of the substrate temperature from 240 K to 80 K during deposition, lead to a broadening of both XPS and NEXAFS signatures, as well as an upward shift of the Si 2p and C 1s binding energies, indicative of a less ordered growth mode at low temperature.

Understanding the ways graphene can be functionalized is of great importance for many contemporary technologies. Using density functional theory calculations we investigate how vacancy formation and substitutional doping by B, N, P and S affect the oxidizability and reactivity of the graphene basal plane. We find that the presence of these defects enhances the reactivity of graphene. In particular, these sites act as strong attractors for OH groups, suggesting that the oxidation of graphene could start at these sites or that these sites are the most difficult to reduce. Scaling between the OH and H adsorption energies is found on both reduced and oxidized doped graphene surfaces. Using the O-2 molecule as a probe we show that a proper modelling of doped graphene materials has to take into account the presence of oxygen functional groups.

In this contribution we inspect the adsorption of H, OH, Cl and Pt on oxidized graphene using DFT calculations. The introduction of epoxy and hydroxyl groups on the graphene basal plane significantly alters its chemisorption properties, which can be attributed to the deformation of the basal plane and the type and distribution of these groups. We show that a general scaling relation exists between the hydrogen binding energies and the binding energies of other investigated adsorbates, which allows for a simple probing of the reactivity of oxidized graphene with only one adsorbate. The electronic states of carbon atoms located within the 2 eV interval below the Fermi level are found to be responsible for the interaction of the basal plane with the chosen adsorbates. The number of electronic states situated in this energy interval is shown to correlate with hydrogen binding energies.

Proton/fluoride spin-lattice (T1) nuclear magnetic relaxation dispersion (NMRD) measurements of 1-butyl-3-methyl-1H-imidazolium hexafluorophosphate, [C4mim][PF6], have been carried out using high field spectrometers and a fast-field-cycling instrument at proton Larmor frequencies ranging from 10 kHz to 40 MHz, at different temperatures. The NMRD profiles are interpreted by means of a simple relaxation model based on the inter- and intra-ionic dipole-dipole relaxation mechanism. Using an atomic molecular-ion dynamic simulation at 323 K the relevant spin dipole-dipole (DD) correlation functions are calculated. The results indicate that the NMRD profiles can be rationalized using intra- and inter-ionic spin DD interactions, however, anions are mainly modulated by ionic reorientation because of temporary correlations with cations, where modulation by translational diffusion plays a minor role. Reorientational dynamics of charge-neutral ion couples (i.e. [C4mim]⋯[PF6]) and [C4mim]+ ions are in the nano-second (ns) time range whereas the reorientation of [PF6]- is characterized by a reorientational correlation time in the pico-second (ps) regime. Based on the NMRD profiles we conclude that the main relaxation mechanism for [PF6]- is due to fast internal reorientational motion, a partially averaged F-F intra- and F-H inter-ionic DD coupling as the anion resides in close proximity to its temporary oppositely charged cation partner. The F-T1-NMRD data display a ns dispersion which is interpreted as being due to correlated reorientational modulations resulting from the H-containing charge-neutral ion couple [C4mim]⋯[PF6]. The analysis of ionicity is based on the free anion fraction, f, and it increases with temperature with f → 1 at the highest temperatures investigated. The fraction is obtained from the H-F NMRD profiles as correlated-non-correlated dynamics of the ions. The analysis of T1 relaxation rates of C, H, F and P at high fields cannot generally give the fraction of ions but is consistent with the interpretation based on the NMRD profiles with relaxation contributions due to DD-intra and -inter, CSA-intra (and -inter for C), including spin rotation for P. The investigation has led to a description of the mechanics governing ion transport in the title ionic liquid via identification of transient correlated/non-correlated ion dynamics.

Recently, it was found that Pt clusters deposited on Pd shell over Au core nanoparticles (Au@Pd@Pt NPs) exhibit unusually high electrocatalytic activity for the electro-oxidation of formic acid (P. P. Fang, S. Duan, et al., Chem. Sci., 2011, 2, 531-539). In an attempt to offer an explanation, we used here carbon monoxide (CO) as probed molecules, and applied density functional theory (DFT) to simulate the surface Raman spectra of CO at this core-shell-cluster NPs with a two monolayer thickness of Pd shell and various Pt cluster coverage. Our DFT results show that the calculated Pt coverage dependent spectra fit the experimental ones well only if the Pt clusters adopt a mushroom-like structure, while currently the island-like structure is the widely accepted model, which follows the Volmer-Weber growth mode. This result infers that there should be a new growth mode, i.e., the mushroom growth mode as proposed in the present work, for Au@Pd@Pt NPs. We suggest that such a mushroom-like structure may offer novel active sites, which accounts for the observed high electrocatalytic activity of Au@Pd@Pt NPs.

Local structures and adsorption energies of a formic acid molecule and its decomposed intermediates (H, O, OH, CO, HCOO, and COOH) on highly electrocatalytically active mushroom-like Au-core@Pd-shell@Pt-cluster nanoparticles with two atomic layers of the Pd shell and stoichiometric Pt coverage of around half-monolayer (Au@2 ML Pd@0.5 ML Pt) have been investigated by first principles calculations. The adsorption sites at the center (far away from the Pt cluster) and the edge (close to the Pt cluster) are considered and compared. Significant repulsive interaction between the edge sites and CO is observed. The calculated potential energy surfaces demonstrate that, with respect to the center sites, the CO2 pathway is considerably promoted in the edge area. Our results reveal that the unique edge structure of the Pt cluster is responsible for the experimentally observed high electrocatalytic activity of the Au@Pd@Pt nanoparticles toward formic acid oxidation. Such microscopic understanding should be useful for the design of new electrochemical catalysts.

Structure and adsorption energy of carbon monoxide molecules adsorbed on the Pt(111) surfaces with various CO coverages in water as well as work function of the whole systems at room temperature of 298 K were studied by means of a hybrid method that combines classical molecular dynamics and density functional theory. We found that when the coverage of CO is around half monolayer, i.e. 50%, there is no obvious peak of the oxygen density profile appearing in the first water layer. This result reveals that, in this case, the external force applied to water molecules from the CO/Pt(111) surface almost vanishes as a result of the competitive adsorption between CO and water molecules on the Pt(111) surface. This coverage is also the critical point of the wetting/non-wetting conditions for the CO/Pt(111) surface. Averaged work function and adsorption energy from current simulations are consistent with those of previous studies, which show that thermal average is required for direct comparisons between theoretical predictions and experimental measurements. Meanwhile, the statistical behaviors of work function and adsorption energy at room temperature have also been calculated. The standard errors of the calculated work function for the water-CO/Pt(111) interfaces are around 0.6 eV at all CO coverages, while the standard error decreases from 1.29 to 0.05 eV as the CO coverage increases from 4% to 100% for the calculated adsorption energy. Moreover, the critical points for these electronic properties are the same as those for the wetting/non-wetting conditions. These findings provide a better understanding about the interfacial structure under specific adsorption conditions, which can have important applications on the structure of electric double layers and therefore offer a useful perspective for the design of the electrochemical catalysts.

Recently (Dvinskikh et al., J. Magn. Reson., 2003, 164, 165 and Dvinskikh et al., J. Magn. Reson., 2004, 168, 194), some of us introduced two efficient solid-state NMR techniques for the determination of heteronuclear dipolar couplings under magic-angle spinning (MAS). These two-dimensional (2D) recoupling methods have been applied previously to simple amino acids, and to columnar systems with high positional and orientational order. In this work, we show that the 2D MAS sequences produce unparalleled H-1-C-13 dipolar resolution in unoriented lipid membranes. The recoupling experiments were applied to hydrated dimyristoylphosphatidylcholine (DMPC) in the liquid-crystalline L-alpha phase, and the results agreed well with previous NMR investigations using specifically deuterated phospholipids.

To slide surfaces against each other with application of a minimum force and minimum wear has been important since ancient times, and it remains equally important today. The use of oil-soluble lubricants is widely spread in technology, whereas living organisms have developed water-soluble lubricants to facilitate sliding motions. In this perspective article we focus on water-based lubrication in the boundary lubrication regime, and particularly lubrication synergies. This focus has, of course, found inspiration from the outstanding lubrication properties of synovial joints. It has ignited significant amount of research, mostly aimed at answering the question: Which molecule is the magic biolubricant? Different research groups have advocated different answers, and the debate has been intensive. In this article we argue that the question in itself is inappropriate. The relevant question is rather the following: How do molecules work in synergy to provide superior lubrication?

Surface affinity, orientation and ion pairing are investigated in mixed and single solute systems of aqueous sodium hexanoate and hexylammonium chloride. The surface sensitive X-ray photoelectron spectroscopy technique has been used to acquire the experimental results, while the computational data have been calculated using molecular dynamics simulations. By comparing the single solute solutions with the mixed one, we observe a non-linear surface enrichment and reorientation of the organic ions with their alkyl chains pointing out of the aqueous surface. We ascribe this effect to ion paring between the charged functional groups on the respective organic ion and hydrophobic expulsion of the alkyl chains from the surface in combination with van der Waals interactions between the alkyl chains. These cooperative effects lead to a substantial surface enrichment of organic ions, with consequences for aerosol surface properties.